1. Field of the Invention
The present invention relates to a displacement sensor comprising a magnetic sensing device such as a Hall IC, and a magnetic field forming device for generating a magnetic field, which is capable of moving relative to the magnetic sensing device. The displacement sensor outputs f from the magnetic sensing device an electric signal having a level which corresponds to the relative displacement between the magnetic sensing device and the magnetic field forming device.
The present invention also relates to a magnetic field forming device for providing a magnetic field in an exterior space using a magnetic member such as a permanent magnet.
2. Description of the Related Art
A position measuring device (displacement sensor) disclosed in Japanese Unexamined Patent Application Publication 2001-263319 comprises a permanent magnet mounted on a movable member such as a drive shaft of an intake exhaust valve of an engine. The position (displacement) of the intake exhaust valve is detected by the permanent magnet and a Hall element. The rod-form permanent magnet is accommodated in a tubular member coupled to an end of the drive shaft, and fixed elastically within the tubular member by an adhesive such as an epoxy resin.
In this type of displacement sensor, finishing of the permanent magnet is difficult, and hence it is difficult to mount the permanent magnet directly onto the movable member such as the aforementioned drive shaft of the intake exhaust valve. Therefore, in the invention disclosed in Japanese Unexamined Patent Application Publication 2001-263319, a constitution is employed whereby the tubular member is attached to the detection subject, and the permanent magnet is accommodated in and fixed to the tubular member. With this constitution, the permanent magnet must be disposed in a prescribed position within the tubular member, typically a position in which the central axis of the permanent magnet matches the central axis of the tubular member (in other words, a coaxial position with the tubular member) . However, with the assembly method described in Japanese Unexamined Patent Application Publication 2001-263319, in which an adhesive is used to fix the permanent magnet inside the tubular member, it is difficult to align the central axis of the permanent magnet with the central axis of the tubular member with precision. Moreover, with this assembly method, a considerable amount of time is required for the adhesive to harden, and hence the assembly process is slow.